They’re talking about myocarditis, not pericarditis. I don’t know how bad the latter is, but I’ve heard that the former is a health emergency. It can apparently cause arrhythmia, tachycardia or even cardiac arrest in worst cases.
Having said that, the news headline does sound a bit alarmist. Nobody ever claimed that vaccines are absolutely safe. It’s always a tradeoff between the risks associated with the vaccines vs risks associated with the diseases it’s trying to prevent. Side effects like myocarditis are handled on a case by case basis.
I took the vaccines and never contracted covid-19. I didn’t suffer any side effects either (apart from the expected fever) - likely the same for the huge majority of vaccine takers. Had I known about these risks then, I would have still opted for the vaccine. The effects of long-covid are that horrifying. Unfortunately, articles like these are giving ammunition to antivaxxers.
It’s also worth noting that there’s a higher chance of getting myocarditis from covid than from its vaccine. In fact, we lost a friend to myocarditis and septicemia caused by covid. His blood had shown signs of a bacteria that’s normally found in the lungs. We later learned that this was due to the severe lung tissue damage caused by covid.